The invention relates to oil production. In one aspect, the invention relates to a post-primary oil recovery process using microorganisms. The invention in another aspect relates to a CO.sub.2 drive in a post-primary oil recovery process.
Petroleum is recovered from underground oil-bearing reservoirs by penetrating the reservoir with one or more wells and permitting the oil to flow to the surface or pumping it to the surface through the wells. When there is sufficient pressure available in the form of an underlying active water drive, gas dissolved in the petroleum, or a high-pressure gas cap over the petroleum, this naturally-present force can be exploited to force the petroleum to the surface. When the reservoir does not have this natural pressure or when it is depleted by recovery of a portion of the oil and gas in the reservoir, oil will not flow naturally to the surface and methods must be devised to recover this residual oil supply. The recovery of oil using the natural reservoir pressure is called primary recovery. Methods of post-primary recovery have been developed to supply additional pressure to force remaining oil to the producing well or to reduce the forces tending to prevent the flow of oil through the reservoir.
One such method of post-primary oil recovery involves the use of surface active agents to decrease the oil-water surface tension. Such surface active agents can be injected into the formation or, under suitable conditions, can be formed in the reservoir itself. One method of forming surfactants in situ is to inject microorganisms which release surface active substances as metabolic products. The nutrients for the organisms must be supplied to the formation. One method for supplying nutrients for the microorganisms is to inject a nutrient-rich substance such as molasses and, in some cases, nitrogen and sulfur containing compounds into the formation. Such a process is disclosed in U.S. Pat. No. 2,807,570 issued to Updegraff on Sept. 24, 1957. The disadvantages of such a process include its high cost and the tendency of the molasses, and therefore microbial growth, to be concentrated near the injection well and not distributed evenly throughout the formation. This results in uneven distribution of microorganism life and surfactant activity within the reservoir and provides an inefficient method of in situ surfactant preparation.
It is thus an object of the invention to provide a post-primary oil recovery process. It is a further object to provide a method of in-situ surfactant production using microorganisms. In one of its aspects, the invention has as its object to provide oil-derived nutrients for microorganisms used in post-primary oil recovery processes.